Peripheral vascular disease (PVD) results from the development of atherosclerosis, which in the lower limbs leads to poor circulation and poor perfusion of leg tissues, a condition called critical limb ischemia (CLI). In severe forms CLI manifests itself with leg pain, inability to walk, ischemic ulcers in the feet and toes, arterial emboli, and, at advanced stage, gangrene. Risk factors include smoking, diabetes, obesity, high blood cholesterol, a diet high in fats, and having a personal or family history of heart disease. In the United States the prevalence of peripheral vascular disease is 3%, with the prevalence of diabetes-induced PVD rising to 2.8%. About 82,000 non-traumatic lower-limb amputations are performed each year among people with diabetes. Clearly, solutions improving the conditions and treatments options for CLI are in need, especially in view of the ever increasing incidents of diabetes-related PVD.
The progression of PVD may be stopped if sufficient blood flow runs through the diseased vessels. Increase in blood flow can be achieved through exercise, which has been shown to be beneficiary to the outcome of disease. Alternatively, blood flow may be increased by continuous or periodical administration of drugs into the blood stream certain drugs that will act either locally or at the distal bed. This can be achieved by the intra-arterial release of angiogenetic or vasodilatatory substances.
Implantable medical devices suitable for the delivery of drug are known per se in the art. Swiss patent No 688 224 discloses an implantable device for the delivery of liquid pharmaceutical drugs in the human body. Other examples of similar devices are disclosed in US 2004/0249365, WO 02/08233, WO 02/083207, DE 4123091, WO 03/089034, GB 2174218 and WO 96/41080, all incorporated by reference in the present application.
In the above-mentioned Swiss patent No 688 224, the disclosed device comprises an axial piston pump. The piston is driven under control in rotation and axial translation. A fluid reservoir is connected to a suction side of the pump. The pump preferably has a ceramic cylinder and piston. A refilling connection for the reservoir is re-sealable. The integral rotary drive has a separate control unit. Pump, reservoir and drive are coaxial in a cylindrical casing. Alternatively the drive is external, a non-contact coupling transmitting rotary motion to the piston. The end face of the cylinder has a cam profile. An eccentric cam follower peg, which produces the axial motion, is attached to the piston. This system is rather complicated as it involves at least two displacements of the piston, i.e. a rotation coupled to a translation. According to this geometry, it is necessary to use specific means to transform the rotation created by the motor into a translation. The disclosed means complicate the construction, are a dysfunction risk and consume energy.
Another prior art pump is known from US patent application 2004/0044332. This publication discloses an implantable device for delivering medicines in liquid form comprising: a reservoir provided with an inlet and an outlet, said reservoir being adapted to expel the liquid; a variable volume chamber provided with an inlet and an outlet, the volume of the variable volume chamber being in particular smaller than that of the reservoir; a first conduit communicating the outlet of the reservoir with the inlet of the variable volume chamber to fill the latter; a second conduit whereof one of the ends is connected on the outlet of the variable volume chamber.
In this prior art, in fact two variable volume chambers are used (one being the reservoir), separated by a valve, and function by using their respective restoring forces to expel a desired quantity of liquid (for example medicine).